1. Field of the Invention
The invention relates to an integrated circuit that can be used as an electrically modifiable non-volatile memory and enables the protection, in reading mode, of at least a part of the data elements that it contains. The invention also relates to a system using such an integrated circuit in order to make this system incapable of being used without the knowledge of a confidential code to inhibit the protection of the memory and hence that of the system.
The invention finds numerous applications in the field of so-called large-scale consumer applications. Examples of such applications include car radios with anti-theft codes, portable microcomputers, video tape-recorders, television sets and, more generally, all electronic devices that have to be protected against theft by a confidential code.
The integrated circuit according to the invention can also be used for the transmission of data elements that are secured by means of the protectable part of the memory.
2. Description of the Prior Art
Up till now, the protection, by anti-theft codes, of electronic devices such as car radios has been done by means of a confidential code specific to the device written in a programmable memory at a determined address. The memory, which is generally of the EEPROM type, is associated with means for locking at least one part of the data elements that it contains, the locking being activated automatically when the memory is no longer supplied with power. The memory could then be unlocked if it receives a command for the writing, at the determined address, of a data element that coincides with the confidential code.
The drawback of this approach lies in the fact that it is possible to detect the address of the confidential code and write a confidential code of one's choice therein. Thus a stolen device can be reused by means of this new code.
One solution to this problem consists in using a microprocessor-based card that ensures a high degree of inviolability. This solution, however, is costly (in terms of the cost of the card and of its reader). This practically rules out its use for inexpensive, large-scale consumer products. Furthermore, the customizing of each device produced, namely the assigning of a specific code word, must necessarily be done by the manufacturer of the microprocessor of the card in view of the confidentiality attached to the procedures for programming these cards.